Plastic pollution is a planetary threat, affecting nearly every marine and freshwater ecosystem globally. In response, multilevel mitigation strategies are being adopted but with a lack of quantitative assessment of how such strategies reduce plastic emissions. We assessed the impact of three broad management strategies, plastic waste reduction, waste management, and environmental recovery, at different levels of effort to estimate plastic emissions to 2030 for 173 countries. We estimate that 19 to 23 million metric tons, or 11%, of plastic waste generated globally in 2016 entered aquatic ecosystems. Considering the ambitious commitments currently set by governments, annual emissions may reach up to 53 million metric tons per year by 2030. To reduce emissions to a level well below this prediction, extraordinary efforts to transform the global plastics economy are needed.

Abstract1. Coastal blue carbon activities are being implemented by a variety of countries, using different approaches. Existing regulatory regimes, including on coastal protection, are still very useful tools to protect and conserve mangroves, seagrasses and saltmarshes, and preserve their carbon value and role. These approaches suffer, however, from 'traditional' issues such as lack of enforcement, human and financial constraints as well as unclear or misguiding government mandates.2. Successes are witnessed using a community-based carbon project approach, ensuring high stakeholder participation via direct or indirect incentive programmes. Comprehensive coastal zone management approaches seem very promising, but success overall, and regarding carbon specifically, are yet to be reported.3. The Paris Agreement has introduced new tools which could serve as means to trigger more and better coastal adaptation and mitigation efforts. Their implementation details are, however, still under negotiation and their impacts can only be expected in a few years.

Marine plastic pollution has emerged as one of the most pressing environmental challenges of our time. Although there has been a surge in global investment for implementing interventions to mitigate plastic pollution, there has been little attention given to the cost of these interventions. We developed a decision support framework to identify the economic, social, and ecological costs and benefits of plastic pollution interventions for different sectors and stakeholders. We calculated net cost as a function of six cost and benefit categories with the following equation: cost of implementing an intervention (direct, indirect, and nonmonetary costs) minus recovered costs and benefits (monetary and nonmonetary) produced by the interventions. We applied our framework to two quantitative case studies (a solid waste management plan and a trash interceptor) and four comparative case studies, evaluating the costs of beach cleanups and waste-to-energy plants in various contexts, to identify factors that influence the costs of plastic pollution interventions. The socioeconomic context of implementation, the spatial scale of implementation, and the time scale of evaluation all influence costs and the distribution of costs across stakeholders. Our framework provides an approach to estimate and compare the costs of a range of interventions across sociopolitical and economic contexts.

The ecological and societal impacts of plastics production, use, and waste are a complex global challenge. Management strategies to mitigate the impacts of plastics, such as recycling, waste-to-energy, and replacement with alternative materials have impacts of their own. Achieving long-term sustainability of plastics use therefore requires considering the externalized impacts of such management strategies. Here, we assessed the literature on the most common plastic waste management strategies to identify their impacts in relation to the Sustainable Development Goals. We reviewed impacts of bans, levies, and taxes; alternative products; recycling; waste-to-energy; plastic recovery; and extended producer responsibility. Our analysis identified a total of 259 measured impacts of plastic waste mitigation strategies, from 113 papers. Ninety-three impacts were negative, 104 were positive, 11 were neutral, and 51 depended on the context of implementation. Consideration of the impacts of both plastic materials and management strategies is necessary to avoid perverse outcomes of plastic pollution mitigation efforts.

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